Focused Ion Beam Energy Filtering for Spot Size and Beam Current
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Solution Overview
Problem
Existing focused ion beam (FIB) systems face challenges in providing charged-particle beams (CPBs) with variable beam currents and energy spreads, which are essential for various semiconductor, material science, and life science applications.
Innovation Solution
The system employs an extractor aperture plate to create axial and off-axis CPBs, with the off-axis beam being chromatically dispersed and filtered to select specific energy spreads. A beam steering deflector directs the selected CPB portion to a workpiece, allowing for variable beam currents and energy spreads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If beam current is limited to suppress Coulomb interactions, then spot size is improved, but beam current is reduced
Solution Approach 1:
The beam is segmented into multiple spatial channels (on-axis and off-axis regions) that can be independently controlled. The off-axis region provides high current for suppressing Coulomb interactions, while the on-axis region provides low energy spread for precise spot size control. This segmentation allows both contradictory requirements to be satisfied simultaneously by distributing different beam portions to different functional regions.
Solution Approach 2:
Different regions of the beam are given different properties: the off-axis region is optimized for high current density while the on-axis region is optimized for low energy spread. This local quality differentiation allows the system to provide both high beam current (for spot size control via Coulomb suppression) and low energy spread (for precise spot size) in different parts of the beam, resolving the contradiction.
2Manufacturing precision
If energy spread is reduced through chromatic dispersion and filtering, then spot size is improved, but beam current is reduced
Solution Approach 1:
The beam is divided into on-axis and off-axis spatial channels. The off-axis channel undergoes chromatic dispersion and filtering to reduce energy spread, while the on-axis channel maintains high current. This segmentation allows the system to provide both low energy spread (for spot size precision) and high beam current by combining the filtered off-axis beam with the high-current on-axis beam.
Solution Approach 2:
A filter aperture acts as an intermediary element that selectively transmits portions of the chromatically dispersed off-axis beam with desired energy characteristics. This intermediary allows precise control of energy spread while maintaining the ability to adjust beam current by controlling the transmission characteristics of the filter aperture.
3Productivity
If beam current is increased for substantial current applications, then productivity is improved, but Coulomb interactions increase
Solution Approach 1:
The high current beam is segmented into on-axis and off-axis regions. The off-axis region is subjected to chromatic dispersion and filtering that reduces energy spread, which in turn reduces the impact of Coulomb interactions. This allows the system to maintain high beam current for productivity while the filtered portion provides reduced Coulomb interaction effects for precise processing.
4Manufacturing precision
If filter aperture is used to select energy spread, then energy spread control is improved, but beam current is reduced
Solution Approach 1:
The system provides multiple beam output modes from a single beam source: high current mode (using on-axis beam), low energy spread mode (using filtered off-axis beam), and combined mode (using both). This multi-functionality allows the filter aperture to be used selectively depending on whether energy spread control or beam current is the priority, resolving the contradiction by making the system adaptable to different operational requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables the delivery of CPBs with tailored beam currents and energy spreads, reducing sputtering and damage to the workpiece while enhancing the versatility of FIB systems for diverse applications.
Implementation Method 1
the CPB lens is operable to focus the axial CPB and chromatically disperse the off-axis CPB
Implementation Method 2
a beam steering deflector operable to deflect the axial CPB or the selected portion of the off-axis CPB to a workpiece
Data Source
AI summary
Charged-particle beam (CPB) optical systems can include a beam acceptance aperture plate defining a first acceptance aperture and at least one second acceptance aperture, situated with respect to a CPB source so that a first CPB is transmitted by the first acceptance aperture and a second CPB is transmitted by a second acceptance aperture. A CPB lens is situated to receive the first and second CPBs from the beam acceptance aperture plate and direct the first and second CPBs towards a filter aperture plate to transmit selected spectral portion of the second CPB. The selected spectral component of the first CPB can be selectively directed to a workpiece by a beam steering deflector along the same axis. In some examples, the first and second CPBs have different beam currents and only one is directed to a workpiece.